Analysis On The Critical Criterion Of Rollover And Its Influence Factors In The LNG Storage Tank

The rollover phenomenon is researched by means of Fluent simulation compulation in this paper. Based on the study, a critical criterion of rollover in the LNG tank is prorosed.Through researchs on the stratification and rollover process in the LNG tank, two adjacent LNG layers which share the same height in the whole tank are cutted off, a two-dimension physical model and mathematical model of the rollover phenomenon in the LNG tank are established. With the Fluent software, the rollover process in the LNG tank is simulated. According to the simulation result, the rollver process is divided into three phases: rollover phase near the tank thin, transfer phase from the tank thin to the center and the formation phase of the new layers.On the basis of the research of the rollover process, the rollover process under different initial density difference is studied. It turns out that the rollover in the LNG tank changes from steady towards violence with the increasing of the initial density difference. In this process, a critical density difference of rollover exists. If the density difference in the LNG tank is lesser than this critical density difference, the rollover in the tank will not take harm to the tank, on the contrary, the rollover may have threaten on the safety of the tank storage if the density difference in the LNG tank is greater than this critical density difference. The critical density difference is defined as the critical criterion of the rollover in the LNG tank. And the critical criterions of the tanks with the capacity of 160000 m~3, 30000 m~3, 5000 m~3 are obtained as 3kg/m~3, 5kg/m~3, 7kg/m~3 for respectively.Under the research of the critical criterion of rollover in the LNG tank, the critical density difference of the same tank with different diameter is studied. And it turns out that small change of the diameter has little impact on the critical density difference of the rollover in the LNG tank. Also, the influence of the layer height is research, and it shows that the critical density difference in the LNG tank with a settled tank capacity adds with the increasing of the layer height.